1. Field of the Invention
The invention is in the field of cryogenic coolers for cooling thermal viewer detectors which has decreased cool down time and holds at the cold level for a longer period using a cold finger with multiple thermal switches.
2. Description of the Prior Art
In the past problems have existed because the length of the cold finger in cryogenic coolers does not always properly match the length of the dewar well within which the cold finger is mounted. The detectors are mounted on the inner dewar wall facing toward the end of the outer dewar which has a transparent window that passes the radiation frequencies to which the detector is sensitive. Previously, the cold finger extends into the inner dewar until it contacts the end of the dewar, and thus also the detector. This contact of the cold finger with the detector has many disadvantages, such as vibrations from the cooler compressor being transmitted to the detector which adversely effects the image detector and which can easily be detected with sound detection equipment even at large distances. Further disadvantages are that the dewars, which are generally made of polished glass, or the cold finger itself may be damaged during the assembly of the cryogenic cooler and the thermal contact of the end of the cold finger with the detector causes thermal losses after cool down due to heat conduction to the cold station through the cold finger and detector closed thermal circuit.
Efforts have been made to fabricate coolers so that the cold finger is very close to but not touching the detector but it has been extremely difficult to maintain the desired separation.
The present cryogenic cooler alleviates most of these previous problems.